Carotenoids are natural pigments that are responsible for many of the yellow, orange, and red colors seen in living organisms. Carotenoids are widely distributed in nature and perform a number of important biological functions, including protecting organisms from photo-oxidative damage. In the human body carotenoids provide powerful antioxidant action. Antioxidants help form the body's defense against free radicals, which develop as a result of normal metabolism as well as from exposure to pollution and other environmental hazards.
Carotenoids also serve as light-harvesting pigments in photosynthesis. Carotenoids, such as lutein, zeaxanthin, astaxanthin, β-carotene and lycopene, and their esters are valuable as feed additives for improving the color of chickens and bred fishes (such as salmon and trout), and many carotenoids are increasingly being used as food additives and dietary supplements for human consumption.
Extracted and/or enriched carotenoids can be used as nutraceuticals, dietary supplements, or pharmaceuticals. The nutraceuticals industry employs liquid organic solvents to extract carotenoids and lipids from natural substrates. Hexane and acetone have traditionally been used for many extractions, especially for carotenoids like astaxanthin. However, because of increasing scrutiny and concerns about safety and toxicity, both solvents are losing favor within the nutraceuticals industry as extractants. Furthermore, it is anticipated that the use of lipid organic solvents for natural products extraction may be strictly regulated in the future, hence there is need for a more acceptable alternative. In any event, after such extraction with organic solvents, distillation is required to remove the organic solvent(s) from the extracted carotenoid fractions. The high temperature required for distilling the final solvent remnants can degrade the sensitive extract. Hexane and acetone are being replaced, when possible, with ethanol or other less toxic liquids; however, even the use of ethanol can harm the sensitive extract during the distillation step when the solvent must be boiled off.
Supercritical fluids and liquefied gases, have been used as gaseous solvents for extracting lipids, essential oils, sterols, and many other classes of compounds from botanical or marine substrates. Carbon dioxide has been used predominantly, but it is not always capable of extracting relatively polar or high molecular weight compounds (such as astaxanthin). Some of the light hydrocarbons, e.g., propane and butane, have been used, but sometimes with only limited success. For example, U.S. Pat. No. 5,789,647 to Heidlas et al., discloses the use of liquefied gases, e.g., propane and butane, to extract carotenoids from various substrates (e.g., vegetable, fungal and fermentation derived substrates) when carbon dioxide does not achieve satisfactory yields. Use of these liquefied gases, was found unsatisfactory in achieving high yields of carotenoids. Despite the addition of organic solvents (called entrainers when used with supercritical or liquefied gases) such as ethanol, acetone, and ethyl acetate to the gas, yields of carotenoids were, occasionally, still low. Reported yields were as low as 60%, in some cases. Besides the low yields encountered, residual organic solvents must still be removed from the extract. Whereas small quantities of ethanol might be acceptable in the final product, traces of entrainers such as acetone and ethyl acetate would not be acceptable in products intended for human consumption or use.
There is a need for an economic and efficient method to extract carotenoids from mixtures that eliminates the use of liquid organic solvents and provides acceptable product yields.